The present invention relates generally to mobile grain harvesting machines and more particularly to a dual rotor axial flow combine in which improved means are provided for separating grain from other crop materials, such as straw.
During field operation of a mobile combine harvester, grain is threshed, separated, cleaned and delivered for transport from the field. Over the past 30 years, the threshing function in most commercially available combines has been carried out by a rotating threshing cylinder cooperatively associated with a concave extending transversely to the direction of combine travel. Crop material is fed to the forward edge of the concave, and passed along a generally longitudinal path between the concave and rotating cylinder. Some grain is discharged through the concave while the remaining crop material is discharged over the trailing edge of the concave onto transverse straw walkers that extend rearwardly across the combine. Grain, separated from the chaff on the reciprocating walkers id deposited on cleaning sieves and eventually collected and conveyed to a grain tank, while the straw residue is advanced rearwardly and expelled onto the field. This type of harvesting equipment commonly referred to as a conventional combine, is more thoroughly described in the prior art, exemplary of which are U.S. Pat. No. 3,411,274 and No. 3,472,235.
During the lengthy period of mobile combine development many other types of combines have been considered but for the most part with a lesser degree of success than the conventional combine. For example, U.S. Pat. No. 2,825,455 issued Mar. 4, 1958, to W. Streich et al, shows a combine in which a conventional threshing cylinder and concave are utilized in combination with a longitudinally extending rotary drum separator in place of conventional straw walkers. Another example of the many and varied arrangements in the prior art is shown in U.S. Pat. No. 2,811,158 issued Oct. 29, 1957 to O. Rietman. In the Rietman patent, a conventional concave and threshing cylinder are again shown in combination with a separation structure utilizing a drum mounted along an axis aligned with the path of combine travel.
Recently, a new and significantly different combine design has been developed and has met with outstanding commercial success. This combine, described in many patents that have issued over the past several years, comprises two side-by-side generally cylindrical crop handling units each having tandem threshing and separating sections. During operation crop material is conveyed to the crop handling units and thence advanced in a generally axial direction along two separate helical paths in the cylindrical units. Exemplary of this type of axial flow combine is U.S. Pat. No. 3,742,686 issued on July 3, 1973, in the name of E. W. Rowland-Hill and assigned to the assignee of the present application. During operation, grain is separated from crop material and discharged through concaves and grates in the threshing and separating sections, respectively, onto a grain pan below the cylindrical units. The grain is in turn deposited on cleaning sieves and thence elevated by an auger to a storage tank mounted on the combine. Meanwhile, the residue is conveyed rearwardly and expelled onto the field. This design, which has reduced grain losses, minimized grain damage and increased overall capacity and reliability, is believed to be the most efficient high performance commercially available combine known in the art.